1. Technical Field
The present invention concerns a safety socket for a light bulb with either a screw cap or a bayonet cap.
2. Discussion
Many electrocution accidents occur when an electric socket provided to receive a light bulb is devoid of such light bulb while being connected to a powered supply line. As safety specifications stipulate that the voltage is applied to the central contact block of the socket, an accident may arise when a finger or a tool such as a screwdriver is inserted into a bulbless socket and makes contact with the central contact block.
In the relatively frequent case where the phase voltage is applied to the contact tube of the socket instead of to the central block as a consequence of an assembling of the socket or of the supply line by an unqualified person, an accident can very easily occur because this contact tube is relatively unprotected from the exterior since it is normally connected to the earthed, or neutral wire conductor.
Similarly, an electrocution accident can occur when a light bulb is broken in a socket and a portion of the electric circuit of the light bulb remains under voltage and is no longer protected by the glass of the light bulb. In this case, likewise, a contact with a finger or a tool can be dangerous.
There are sockets provided with a hand-operable switch allowing to cut off the supply circuit of the central contact block. Since in a general manner these switches are rotary switches, it is not possible for the user to know if the supply circuit of the central contact block is cut off of not. The switch of such a socket is rather intended to turn the light on or off rather than to operate as a safety device.
The application EP-A-0 744 792 discloses a socket provided with a safety disc that descends when the light bulb is inserted into the socket. The safety disc is provided with a traversing contact to ensure the connection between the contact at the bottom of the cap and a contact block having the phase voltage. This embodiment corresponds to the closest prior art of the invention which is introduced in the preamble of the independent claims. In this document, the safety disc is provided with another traversing contact for the passage of the earth line, this contact being made in connection with a flexible conductive blade pushing against the thread of the light bulb. This conductive blade represents a danger for the user because it is easy, when there is no bulb in the socket, to bend this blade with the fingers or with a tool and to make it alive, in particular in the case where the phase and neutral wire conductors have been inverted,
The application EP-A-0 027 244 describes a socket provided with a safety device having a very complicated construction, thus being little reliable in use. As mentioned previously, a movable conductive blade is provided to ensure the connection to the neutral with the same drawback as that mentioned previously.
A first object of the invention is to propose a safety socket for a light bulb provided with a safety device allowing to avoid an accidental contact with any accessible conductive part of the socket.
A second object of the invention is to propose that the preceding safety socket is provided with a safety device able to operate whatever the manner in which said socket is connected to the supply fine.
Another object of the invention is to propose a safety socket provided with a safety device of simple design and reliable in use.
Another object of the invention is to propose a safety socket provided with a safety device with redundant safety.
Still another object of the invention is to propose that the safety socket is provided with a lockable safety device.
Furthermore, transition sockets are known that allow fitting a light bulb provided with a cap having a determined diameter into a socket having an equal or different diameter.
On this basis, another object of the invention is to propose a transition socket provided with one or another of the above-mentioned safety devices.
These objects have been achieved by a safety socket of which a first embodiment is described in claim 1 whereas a second embodiment is described in claim 2, particular embodiments or variants being described in the dependent claims.
Several embodiments and variants of a safety socket according to the present invention are described in detail below, this description further mentions other advantages of the invention, and should be considered with respect to the annexed drawings comprising the Figures in which: